The inventive concepts described herein relate to magnetic tunnel junction devices and, more particularly, to magnetic tunnel junction devices that are used in magnetic random access memory (MRAM) devices.
Recently, MRAMs that use the magnetic resistance effects of ferromagnetic materials to store data have been identified for potential use as next-generation solid-state nonvolatile memories because of their potential to support fast read and write times while providing large storage capacity and low operating power requirements. Magnetic tunnel junction (MTJ) devices that have ferromagnetic tunnel junctions are of particular interest because of the large variation in magnetic resistance exhibited by such devices.
A ferromagnetic tunnel junction may comprise a stack of at least three layers that includes a storage layer, an insulation layer and a fixed layer that maintains a specific magnetization orientation. When a current is introduced into the ferromagnetic tunnel junction device, the current may tunnel through the insulation layer. When this tunneling occurs, a resistance of the junction is changed according to a relative angle of the magnetization orientations of the storage layer and the fixed layer. If the magnetization orientations of the fixed layer and the storage layer are parallel, the junction resistance is minimized. But if the magnetization orientations are anti-parallel, the junction resistance is maximized. Such resistive change is referred to as a tunneling magneto-resistance effect (TMR). By using a magnetoresistive device that has such a ferromagnetic tunnel junction as a memory cell, the memory cell is capable of holding information in which the binary codes ‘0’ or ‘1’ correspond to the parallel and anti-parallel states of the storage layer and the fixed layer.
To program or “write” data into a magnetic tunnel junction device, a spin transfer writing mechanism that uses spin angular momentum migration may be used. With this mechanism, a spin polarization current may be allowed to flow into the MTJ device, and this current forces a magnetization orientation of the storage layer to be reversed. MRAM devices that include MTJs may exhibit high integration density and low power consumption, and may easily induce magnetization inversions of magnetic materials.
The use of magnesium oxide (MgO) as an insulation layer of an MTJ device has theoretically been proposed as a means for obtaining a high magnetic resistance ratio (i.e., the ratio of the minimum and maximum junction resistances). By crystallizing MgO, electrons with a specific wave number may be selectively tunneled into a ferromagnetic layer. During this tunneling, a spin polarization rate is larger for a specific crystallization orientation, resulting in a high magnetic resistance ratio. In an MTJ device, a larger magnetic resistance ratio may correspond to higher integration density and lower power consumption.
A spin transfer type (STT) MRAM is known in the art that uses a manganese-gallium (MnGa) of L10 structure for a ferromagnetic layer (the MnGa layer may be used as the storage layer or the fixed layer), as disclosed in Japanese Patent Publication No. 2012-204683. However, since MgO and MnGa are not harmonized with each other in crystal lattice architecture, the lattice mismatch can degrade the magnetic characteristics of such a device.
Japanese Patent Publication No. 2012-204683 proposes a solution for the lack of lattice harmonization between MnGa and MgO, as follows. That solution is to adopt MgAlO for the non-magnetic tunnel barrier layer and MnAl as an interface layer of the tunnel barrier layer.